1. The Field of the Invention
The present invention relates to color management. More particularly, embodiments of the invention relate to systems and methods for performing black generation to maximize color gamut of the device.
2. The Relevant Technology
Color devices such as digital cameras, scanners, monitors and printers are able to produce a wide range of vibrant colors. It is often the case, unfortunately, that the rich color of a digital picture changes when that same image is printed. It may even look different when displayed on a monitor. The primary reason for this change is that each device has a different color gamut and each device often processes colors differently. As a result, a noticeable color shift may occur as the color data from the first device is rendered by the second device.
One of the ways that this problem has been addressed is through the use of color management systems that include, for example, ICC (International Color Consortium) profiles. ICC profiles are used to convert data from a source device to data that is compatible with a destination device. The ICC profile effectively creates a bridge that enables the data to be successfully converted from one color space to another color space. One of the ways that color management systems characterize each device is by creating a relationship between the device color space and a device independent color space such as CIE L*a*b* (LAB).
In a common scenario, data from the color space of an input device is converted to the device independent color space using a forward transform. Next, the data in the device independent color space is converted to the color space of the output device using an inverse transform. For most printing applications, an inverse transform is essential because the data being printed usually originates from a device with a different color gamut.
While the inverse transform may seem to be straightforward, it can be a complex process. In fact, the inverse transform becomes much more complicated when a fourth primary color is added to the mix. For example, RGB (Red, Green, Blue) to CMY (Cyan, Magenta, Yellow) conversions are usually less complicated than RGB or CMY to CMYK (Cyan, Magenta, Yellow, Black) color conversions. The addition of a fourth dimension introduces complications to the color conversion process and in particular to the inverse transform that is required in the color management system.
While CMY primaries are theoretically sufficient to produce all of the desired colors that may be needed, a fourth primary color, which is black (K) in this instance, is often added. Adding K to the printing system has several advantages including improving the dark color region gamut, saving the CMY inks for neutrals which can reduce costs, and the like.
Even though the addition of K has significant advantages, the inverse transform becomes more complicated because the same device independent color can be obtained in numerous ways with CMYK primary inks. However, a unique transform is required in an inverse transform.
Conventional methods for converting CMY to CMYK, however, require a procedure for adding K. For instance, the addition of K has been conventionally achieved using various under color removal (UCR) and gray component replacement (GCR) strategies. A simple UCR solution, for example, is to find the minimum of the CMY primaries and to replace that minimum with black. Other solutions use a function of the CMY minimum to add black and a different function of the CMY minimum for the removal of the gray component from the CMY amounts.
These functions generate one dimensional look-up tables or curves called GCR or UCR curves. The drawback to these solutions is that they restrict the gamut too much or introduce unwanted black in light regions of the gamut. The presence of black dots, for example, can draw unwanted attention and detract from the smoothness of the printed image. Systems and methods are needed for black generation to maximize the gamut while using CMYK primaries, but which do not reduce the quality of the printed image.